Nick Clegg will on Monday attempt to establish a cross-government task force to improve mental health services throughout the country.

The deputy prime minister who has a history of campaigning for mental health will say at his monthly press conference that Britain needs to redouble its efforts to tackle mental health which costs the country £100bn a year.

The mental health taskforce, which will be chaired by Clegg and includes senior ministers such as Theresa May, Jeremy Hunt and Vince Cable, is to examine urgently how to improve mental health services for young people and to improve crisis care. The deputy prime minister is concerned by the large number of people with severe mental illness who end up in police cells and prisons.

Clegg, who announced at the Liberal Democrat conference that the government would introduce the first waiting time standards for mental health in April, will point out that the government has built a strong foundation for the improvement of services through its mental health strategy. He will cite the £400m investment expanding talking therapies.

But the deputy prime minister will say that more needs to be done to target help at the young after figures showed that three children in every classroom have diagnosable mental heath conditions. He will say that only a quarter of people with a common mental health problem receive treatment while 90% of prisoners have at least one mental health disorder.

Clegg, who will say that mental illness costs the country £100bn in lost working days, benefits and treating preventable illness, said: “Mental health affects every aspect of our lives. One in four people in the UK will experience a mental health problem and it costs the country more than £100 billion. This is too big an issue for the NHS to deal with alone. The whole of government needs to combine its efforts and pool its resources to help the millions of people whose mental health condition is preventing them from getting on in life.

“For far too long mental health has been in the shadows and many people have suffered in silence as a result. It is time to turn a corner on outdated attitudes and bring mental health issues out into the open. It is time that the whole of society started providing the care and support to those with mental health conditions in the same way that they would to those with a physical condition.”